Chang 1986 Aquacultural-Engineering

7/28/2019 Chang 1986 Aquacultural-Engineering

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Aquaculmral Engineering 5 i l 9 8 6 3 2 5 3- 2 7 0

Systematic Ap proach of Sea-Farming inPenghu, Taiwan, RO CKun-Hsiung Chang

I n s ti tu t e o f Z o o l o g y , A c a d e m i a S i n ic a , T a i p e i. T a i w a n 1 1 5 . R O C

andJen-Chyuan Lee

C o u n c i l o f A g r i c u lt u r e ,T a i p e i , T a i w a n 1 0 7 , R O C

A B S T R A C TU nder the po l i O ' o f exp lo i t ing a m bie n t resources , farm ing the sur -r o u n d in g w a ter s h a s r ecen t ly b eco m e o f n ew imp o r ta n ce i n Ta iw a n.Curren tly , the m ain ques t ion to be answ ered is wha t k ind s o f sea -farm ing can be app l ied toge ther op t im al ly in the sa m e waters ? A sys te -ma t ic approa ch was there fore in it ia ted in 1982 in an a t tem pt to co l lec tin form at ion on s ea- farm ing prac t ice in three consecu t ive years . 77zispaper repor t s on the resu l t s ob ta ined a t Datsang Ba); Penghu , dur ingthe f irs t tw o ) 'ears.

hz the presen t s tudy , the Jo l lowing sea- farnz ing m etho ds wereapplied ." long-l in e o yster cul ture, ar t i f ic ia l reef em pla cem en t , an d f ish -cage culture.In s p it e o f t h e l o w co n cen t r a t io n o f n u tr i en ts a n d p h y to p la n k to n , t h egrow th o f oys ters cu l t iva ted by long- l ine cu l ture sys tenzs was Ja ir ly go od

in com par iso n wi th those cu l t iva ted a long the wes tern coas t o f Ta iwan .The h igh COD vahzes in sed imen ts accompanied by low nzz t r ien ts inthe waters sugge sted that the ma terials exc reted by oysters w eredegraded , bu t the degrad ing ra te w as s low. However , the d i s so lvedoxygen in the wa ter main ta ined a t l eas t 80% sa tura t ion which i s su i t -ab le fo r the oys ter cu l ture in the loca l wa ters . The f i sh spec ies cu l t iva tedin cages inchzde groupers , sen -bream, snappers , emperor , and rudder -

2 5 3Aquacultural Engineering 0 1 4 4 - 8 6 0 9 / 8 6 / S 0 3 . 5 0 - E l s ev ie r A p p li ed S c i en cePubl i shers Ltd , England , 1986 . Pr in ted in Great Br i ta in


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254 K . -H . C h a n g , J . -C L eef is h . A f t e r t h e y w e r e c u l ti v a t e d f o r a p e r i o d o f I 0 t o 1 6 m o n t h s , t h eh i g h e s t s u r v iv a l r a te w a s a t t r ib u t e d t o g r o u p e r s ( 8 1 " 4 % ) , w h e r e a sm d d e r f i s h h a d t h e l o w e st , th a t w a s, o n l y 38 " 4% o f n t d d e r f i s h i n d i -v i d u a l s s u r v i v e d . P r o s p e r o u s o r g a n i s m s a r o u n d a r t i f i c i a l r e e f s i n t h ep r e s e n t s t u d y w e r e s i m i l a r to t h o s e f o u n d a r o u n d t h e r e e f e m p l a c e d a tS o u k a n g , a l s o i n D a t s a n g B a y . i n 1 9 7 7 , T h e w a v i n g a t t d t h e s h a d o w o fl o n g - l i n e s h a n g i n g o n o y s t e r c u l t u r e s y s t e m s o v e r t h e a r t i f i c i a l r e e f ss e em ed no t to a f f ec t the i r ef fec ti venes s. Pre sen t w or k a l so sugges t s tha tt h e st u d y o f t h e i n t e ra c t io n b e t w e e n t h o s e c t d tu r e a p p l i c a t i o n s a n d t h ee n v i r o n m e n t w o u l d p r o vi d e m e a n i n g l i d d a t a f o r s e a - fa r m i n g i n t h ef i tt u r e a n d w o t d d b e w o r t h w h i l e f o r c r e a ti n g a c o m m e r c i a l l y v ia b leo p e r a t i o n .

INTRODUCTIONUnder the policy of exploiting the ambient resources, farming the sur-rounding waters has recently become of new importance in Taiwan.With the support of the Council of Agriculture (formerly the Councilfor Agricultural Planning and Development), and the National ScienceCouncil, scientists of the Institute of Zoology, Academia SinicaNational Taiwan University, National Sun Yat-sen University, and theTaiwan Fisheries Research Institute have been developing techniquesfor producing animal protein from the sea. Among these techniques,long-line oyster culture, fish-cage culture, and construction of artificialreefs are the most promising.The productivity of the water column must be evaluated beforeinvestment is made. Primary production assumes a main role for theenergy supplier. Subsidies are used to alleviate the pressure from limit-ing factors in the environment. For example, when artificial reefs areemplaced on the sandy bottom, demersal animals and fouling organ-isms which settle down around those reefs will have a better chance ofsurvival because the latter are produced with space and substrateswhich meet these organisms' needs. The amount of space in waterdedicated to sea-farming varies according to the target organism andthe farming method, e.g. fish-cage culture occupies the water surfaceand upper column of the sea, whereas long-line oyster culture extendsfrom the water surface to the lower column of the sea to gain a greaterbenefit.

Nowadays establishing sea-farming has proved to be an efficientway to increase coastal fisheries production. However, productivity


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Systematic approach o f sea-farming in Penghu. TaiwatL R O C 255u l ti m a t e ly d e p e n d s u p o n t h e c a r o ' i n g c a p a c i ty o f t h e s ea . T h e q u e s t i o no f w h a t k i n d s o f s e a - f a r m i n g c a n b e o p t i m a l l y u s e d t o g e t h e r i n t h es a m e w a t e r s h a s b e c o m e a n i m p o r t a n t i s s u e . A s y s t e m a t i c a t t e m p t i st h e r e f o r e m a d e i n t h e p r e s e n t s t u d y to c o l le c t i n f o r m a t i o n o n d i f fe r e n ts e a - f a r m i n g m e t h o d s , s u c h a s l o n g - l in e o y s t e r c u l tu r e , f is h - c a g ec u l tu r e , a n d a rt if ic ia l r e e f e m p l a c e m e n t o v e r t h r e e c o n s e c u t i v e y e a r ss in c e th e a u t u m n o f 1 9 8 2 . T h i s p a p e r r e p o r t s t h e r e su l ts o f o u r s t u d yo v e r th e p a s t t w o y e a r s .

D E S C R I P T I O N O F T H E S T U D Y A R E AP e n g h u , a l s o c a l l e d t h e P e s c a d o r e s I s l a n d s , c o m p r i s e s a g r o u p o fi s l a n d s w i t h e x t e n d e d s e r r a t e d c o a s t l i n e s a n d s h a l l o w b a y s . T h eT r o p i c o f C a n c e r l ie s a c r o s s t h e m , a n d t h e y a re s u r r o u n d e d b y w a r mw a t e r s . T h e w a t e r s a r e h a r d l y p o l l u t e d b e c a u s e t h e p o p u l a t i o n i sl i m i t e d a n d t h e d e v e l o p m e n t o f i n d u s t r y i s s p o r a d i c . T h e p o t e n t i a l o fm a r i c u l t u r e a r o u n d t h e s e i sl a n d s w a s e s t i m a t e d t o b e h i g h , a n d a s e r ie so f e c o l o g i c al s u r v e y s h a v e b e e n c o n d u c t e d f r o m t h e i n te r ti d a l r e g io nd o w n t o 1 0 m s u b l i tt o r a l o v e r t h e p a s t fi ve y e a r s ( C h a n g e t a l . , 1 9 8 1 .1 9 8 2 ; H s i e h e t a l . , 1 9 8 1 ) . T h e m a i n i s l a n d s , w h i c h a r e p o s i t i o n e d l i k ea p a i r o f b r a c k e t s , h a l f e n c l o s e a w a t e r m a s s c a l le d D a t s a n g B a y (F ig .1 ) . D a g u o y e h i s a v i l l a g e l o c a t e d o n t h e n o r t h w e s t e r n s t r e t c h o fD a t s a n g B a y ( F i g . 1 ). O n t h e s h o r e o f th i s v il la g e a b r e a k w a t e r o f 8 0 me x t e n d s i n t o t h e w a t e r . A l o n g t h e s u r g e z o n e o f t h e s h o r e l i n e , c o r a l sa n d s e a g ra ss a r e d i s t r ib u t e d . F i s h f a u n a o n t h e r e e f s u b s t r a t u m c o n -s is ts m a i n l y o f d a m s e l f i s h e s , g r o u p e r s , a n d b l e n n i e s .

I n P e n g h u , t y p h o o n s u s u a ll y o c c u r f r o m J u n e t o S e p t e m b e r , c a u s i n gs u r g e s t h a t a g i t a t e t h e b o t t o m s a n d , c l o u d t h e w a t e r , a n d d a m a g e t h es u b s t r a t e f l o a t i n g o n t h e w a t e r s u r f a c e . T h e s e a w e e d i s a l s o v i o l e n t l yr e m o v e d f r o m t h e su b s t r at e . S a n d - d r i f t w h i c h r e su l ts i n b u r y i n g o fb o u l d e r s w ill d a m a g e s o m e i n v e r t e b r a te s ' h a b i ta t a s w e ll . N o r t h e a s tm o n s o o n s p r e v a i l i n g i n t h e w i n t e r a l s o c a u s e u n f a v o r a b l e c o n d i t i o n sf o r m a r i n e a n i m a l s . G e n e r a l l y s p e a k i n g , in s p ri n g a n d e a r ly s u m m e rt h e o c e a n is c a l m e r t h a n i n a u t u m n a n d w i n te r .W a te r te m p e r a t u r e r e m a i n e d in a r a n g e b e t w e e n 1 7 C a n d 2 8 Cf r o m M a r c h 1 9 8 3 t o A u g u s t 1 9 8 4 , w i t h t h e l o w e s t , 1 7 C , i n J a n u a r y ,a n d t h e h i g h e s t , 2 8 C , i n J u l y . S a l i n i t y o f t h e s e a w a t e r r e m a i n e d i n ar a n g e b e t w e e n 3 2 a n d 3 6 % 0 - - l o w e s t in A p r i l a n d h i g h e s t i n A u g u s t .


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2 5 6 K.-H. Chang, J.-C Lee

.-,C LOC

1

F i g. 1. M a p s h o w i n g t h e a r e a w h e r e t h e s e a - f a r m i n g s e t - u p w a s l o ca t ed . A b b r e v i a -t io n s : F C C - - F i s h - c a g e c u l t u r e ; L O C - - L o n g - l i n e o y s t e r c u l t u r e ; A R - - A r ti fi c ia lr e e f .

T h e w a t e r w a s q u i t e t u r b i d . T h e t r a n s p a r e n c y m e a s u r e d b y t h eS e c c h i d i s k m e t h o d g e n e r a l l y r a n g e d b e t w e e n 3 a n d 4 m , e x c e p t i nM a y w h e n a v a l u e o f 6 m w a s r e c o r d e d . I n t h e w a t e r n e a r t h e s eab o t t o m t h e t u rb i d i ty i n c r e a s e d .

A s e m i - d i u r n a l t i d a l c u r r e n t p r e d o m i n a t e s i n t h e s t u d y a r e a . T h ec u r r e n t m o v e s f r o m s o u t h t o n o r t h w h e n t h e t i d e i s o n t h e f l o w , a n dvice versa d u r i n g t h e e b b t id e . T h e g r e a t e st c u r r e n t v e l o c i ty r e c o r d e di n t h e p r e s e n t s t u d y w a s 0 -8 m s - L d u r i n g a fl o o d t i d e . H o w e v e r , t h e


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S y s t e m a t i c a p p ro a c h o f s e a - fa rm in g in P e n g h u , T a iw a n , R O C ..~"~~,,a c t u al g r e a te s t v a lu e m a v b e h i g h e r b e c a u s e o f i n c o n s i s t e n t m e a s u r e -m e n t i n t h e p r e s e n t s tu d y .V e l o c i t y d a t a a l s o s h o w e d t h a t t id a l c u r r e n t s f l o w e d f a s t e r ins u r f a c e w a t e r t h a n a t t h e b o t t o m , i . e . m o r e o f t h e s u r f a c e w a t e r w o u l db e r e p l a c e d w h e n t id e s f lo w e d .

W A T E R Q U A L I T YF o r t h e p u r p o s e o f u n d e r s t a n d i n g t h e e f f e c t o f s e a - f a r m i n g o n l o c a lw a t e r s , w a t e r q u a l i t y w a s m o n i t o r e d t h r o u g h o u t t h e e x p e r i m e n t .W a t e r s a m p l e s c o l l e c t e d w e r e a n a l y z e d t o r e v e a l c o n c e n t r a t i o n s o fd i s so l v e d o x y g e n ( D O ) , S iO 2 - Si , P O ~- P, N H ~ - N , N O 2 - N , N O 3 - Na n d c h e m i c a l o x y g e n d e m a n d ( C O D ) . A d d i ti o n a ll y , e x a m i n a t io n o fb a c t e r i a i n t h e s e d i m e n t s w a s c o n d u c t e d . B e n t h i c o r g a n i s m s w e r es a m p l e d , a n d t h e ir a b u n d a n c e e s ti m a t e d .R e s u l ts o f th e s e e x a m i n a t i o n s a r e s u m m a r i z e d a s fo l lo w s :1. Dissolved oxygen (DO): C o n c e n t r a t i o n s o f d i ss o l v e d o x y g en ( D O )d e t e c t e d b e t w e e n M a r c h a n d A u g u s t 1 9 8 3 r e m a i n e d in a ra n g eb e t w e e n 5 "1 m g l it e r - J a n d 6 -2 m g l it e r- ~ . T h a t m e a n t n e a r l y 8 0 %s a t u r a t i o n w a s r e a c h e d d u r i n g t h e i n v e s t i g a t i o n p e r i o d . I n t h o s es a m p l i n g s it es w h e r e c u r r e n t w a s o n t h e f lo w , h o w e v e r , t h e D O c o n -c e n t r a t i o n w a s h ig h e r. T h e c o n c e n t r a t i o n n e a r t h e b o t t o m w a s lo w e rt h a n t h a t a t t h e w a t e r s u rf a c e , b y a v a l u e o f 0 - 0 . 1 m g l i t e r -2. SiO,-Si concentrations: L o w c o n c e n t r a t i o n s a p p e a r e d i n t h es u rf a c e w a t e r i n J u n e a n d J u l y 1 9 8 3 , a n d in t h e w h o l e w a t e r c o l u m n i nA p r i l , M a y , a n d J u n e 1 9 8 4 . I n t h e s e c a s e s , S i O , - S i c o n c e n t r a t i o n s o fl e ss t han 1 ppm ( 35"6 ~ g a t li t e r - ~ ) w er e t yp i ca l l y f oun d .G e n e r a l l y t h e c o n c e n t r a t i o n s o f th i s e l e m e n t v a r i e d s e a so n a ll y . F ore x a m p l e , i n J a n u a r y 1 9 8 4 a s h i g h a s 1 -5 p p m w a s r e c o r d e d ; t h e n th ec o n c e n t r a t i o n s d e c r e a s e d i n M a r c h , d r o p p e d t o t h e l o w e s t ( n e a r l yz e r o ) i n A p r i l, a n d r e m a i n e d l o w in M a y a n d J u n e . W h e r e a s i n t h e fo l-l o w i n g m o n t h s , n a m e l y Ju l y a n d A u g u s t , t h e c o n c e n t r a t i o n s i n c r e a s e d ,a n d n e a r ly 1 .6 p p m w a s r e a c h e d .3. PO4-P concentrations: T h e c o n c e n t r a t i o n s o f P O 4 - P i n v es ti g at e df r o m M a r c h t o S e p t e m b e r 1 9 8 3 w e r e m o s t ly h ig h e r t h an 0 -5 p pm .H o w e v e r , i n t h e n e x t y e a r t h e c o n c e n t r a t i o n s w e r e l o w e r , i . e . n e a r l yn o t h i n g w a s d e t e c t e d i n J a n u a r y , a n d f r o m M a r c h t o A u g u s t th e c o n -


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2 5 8 K.-H. Chang, J.-C. Leecentrations kept in a range of 1-4 ppb* (0.03-0.13 ~g at liter -L)except in June when a value of 7 ppb was found in PO~-Pconcentrations in the bottom water.4. NH~-N concentrations: Significant variation characterized therange of concentrations of NH4-N in the local waters. In December1983, the concentrations of NH4-H in the bottom water was 407 ppb(29.1 ug at li ter- ~), with a value of 311 ppb (22.2 .ug at liter -~) in thesurface water. Then the concentration decreased gradually andreached the lowest value, i.e. less than 10 ppb, in March. Thereafterthe content of NH~-N increased throughout April, May, and June, toreach a concentration of 57 ppb in June. The concentration droppedagain after June, and in August it maintained a level of about 10 ppb.5. N O 2 -N concentrations: In August 1984 the NO,-N concentrationreached its highest value at 21 ppb (1"5 ,ug at liter -~) in the surfacewater and 14 ppb (1"0 ~g at liter -~) in the water near the bottom. Inthe other months the concentrations were much lower, i.e. generallykept in a range of 1-2 ppb (0.07-0"14 j2g at liter-~).6. NO.~-N concentrations: Data of the concentrations of NO3-Nexamined from April to August 1984 revealed that during June andJuly the concentrations were about 5 ppb, a value much lower thanthose in April, May, and August, when the concentrations were 20ppb (1'4 t2g at liter-~) in the former two months and 15 ppb in thethird month.7. Ch emical oxygen dem an d (COD): Examinations were conductedfrom December 1983 to August 1984 which showed the highest valuewas 5.9 ppm in January, with lower values of about 3 ppm in summer.8. N um be r of bacteria: Data collected from May to August 1984showed that in the water column there were about 2 x 10 -~ bacteriaml- ~ of water, whereas in the sediment there were about 2-10 x 106individuals ml - t of bacteria.9. B enth ic organisms: Organisms in the sediment were recorded byeight examination samples collected by an Ekman-Birge collector(15 cm x 15 cm). These organisms consisted of polychaetes, oLigo-chaetes, shrimps, crabs, amphipods, and others (Table 1). Polychaetesand shrimps were the major components of the biota from April toJuly 1984.* p p b = p a r t s p e r b i l l i o n i b i l l i o n = 1 0 - " ) .


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Systematic approach of sea-farming in Pengh,~. Tai~an, R O CT A B L E 1

A b u n d a n c e o f t h e B e n th i c O r g a n i s m s S a m p l e d a t D a g u o y e h i in d /0-18 m - ') , 1984

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Po l yc hae t e s 51 45 19 12 29O l igo ch ae tes 1 "~ 0 1 1Sh r i m ps 38 9 14 15 25C r abs 0 0 4 6 6A m p h i p o d s 5 0 7 0 2O th er s 0 "~ 6 7 4T o t a l 9 5 5 8 5 0 4 1 6 7

P H Y T O P L A N K T O NP h y t o p l a n k t o n i n t h e s t u d y a r e a w e r e in v e s ti g a te d f r o m M a y 1 9 8 3 toJ u l y 1 9 8 4 . I t a p p e a r e d t h a t c e ll d e n s i t ie s o f p h y t o p l a n k t o n r a n g e df r om 0 - 8 7 - 1 ' 1 8 1() -~ c e l ls l it e r - t i n A ugu s t 1983 t o 4 l 0 s c e l lsl it e r- ~ i n F e b r u a r y 1 9 8 4 . I n 1 9 8 4 , e x c e p t in F e b r u a r y a n d J u l y , t h ea b u n d a n c e o f p h y t o p l a n k t o n k e p t i n t h e r a n g e 4 - 6 10* c ell s l i te r -d u r i n g t h e e x a m i n a t i o n p e r i o d . T h e e x c e p t i o n w a s 1 '5 1 0 a c e ll sl i t e r -t in J u ly . A n a p p a r e n t i n c r e a s e o f p h y t o p l a n k t o n a b u n d a n c e i n1 9 8 4 w a s s h o w n b y c o m p a r i s o n w i th th e s a m e m o n t h o f th e p r e v io u sy e a r; in M a y 1 9 8 4 t h e a b u n d a n c e o f p h y t o p l a n k t o n w a s sLx t im e sm o r e t h a n t h a t in th e s a m e m o n t h i n 1 9 8 3 . V a r ia ti o n s o f p h y t o -p l a n k t o n d e n s i t i e s b e t w e e n s a m p l i n g s t a t i o n s a n d w a t e r d e p t h s w e r ea l s o o b s e r v e d . G e n e r a l l y , t h e a b u n d a n c e o f p h y t o p l a n k t o n i n t h e a r e aw h e r e t h e l o n g - l i n e o y s t e r c u l t u r e w a s l o c a t e d w a s l e s s t h a n t h a ti n v e s t i g a t e d e l s e w h e r e . P h y t o p l a n k t o n i n t h e c o l l e c t e d w a t e r s m a i n l yc o n s is te d o f d i a t o m s w h i c h w e r e r e p r e s e n t e d b y Thalassisira spp . ,kicrn orp ho ra abb reviata, Ple uro sigrn a aff ine, Skeletonerna costatum ,a n d Chaetoceros sp . Pleurosigma affine, w h i ch w as u n c o m m o n a r o u n dT a i w a n , p r e d o m i n a t e d in th e s a m p l e s c o l l e c t e d in J u l y a n d A u g u s t .T h e f a c t o r s a f f e ct i n g t h e m a s s o c c u r r e n c e o f t h is d i a t o m i n t h e lo c a lw a t e r s r e m a i n t o b e s tu d i e d a n d d i sc u s s ed .


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2 6 0 K.-H. Chang , J . -C . LeeA P P L I C A T I O N O F S E A - F A R M E N G

T h e s e a - f a rm i n g t e c h n i q u e s u s e d i n t h e s t u d y i n c l u d e l o n g - li n e o y s t e rc u l t u re , a r t if ic i a l r e e f e m p l a c e m e n t , a n d f i sh - c a g e c u l t u r e ( F ig . 2 ).Lon g- l ine oyster cu l tureT h e o y s t e r , a f i l t e r - f e e d e r , i s a n i m p o r t a n t s o u r c e o f p r o t e i n f r o m t h es e a . A p l a s ti c c o m p a n y w h o t r i e d t o c u l t i v a te o y s t e r s i n d e e p w a t e r i nP e n g h u i n 1 9 7 5 i n i t ia t e d l o n g - f i n e c u l t u r e s y s te m s . W i t h s o m ei m p r o v e m e n t s , t h e s e c u l t u r e s y s t e m s w e r e r a p i d l y e x p a n d e d i n t h el o c a l w a t e r s , a n d a s a r e s u l t p r o d u c t i v i t y i n c r e a s e d . L i n a n d T a n g( 1 9 8 0 ) m a d e a b a s ic s t u d y o f t h e c u l t u r e d o y s t e rs o f P e n g h u f r o m t h ev i e w p o i n t o f p o p u l a t i o n e c o l o g y . I n t h e l o n g - l i n e c u l t u r e s y s t e m , 1 0b u o y s w e r e c o n n e c t e d b y f o u r p a ra l le l r o p es . T h e s e r o p e s w e r e 4 5 mi n l e n g t h a n d 3"5 c m i n d i a m e t e r . T h e r o p e s w e r e a r r a n g e d a b o u t3 0 c m a p a r t . I n 1 9 8 3 , 1 0 l o n g - l i n e c u l t u r e s y s t e m s w e r e i n t r o d u c e d ; in1 9 8 4 , 1 4 w e r e s e t u p . I n e a c h s e t t h e r e w e r e 5 0 0 s t ri n g s o f o y s t e rs .T h e w h o l e sy s t e m w a s s e c u r e d a t e a c h e n d w i t h a 6 0 k g a n c h o r.

S i n c e s p a t c o l l e c t i o n w a s n o t p o s s i b l e i n P e n g h u , a ll th e s p a t s w e r ep u r c h a s e d f r o m o y s t e r f a r m e r s o n t h e w e s t e r n c o a st o f T a i w a n i n m i d -J a n u ar y . T h e s p a ts s e t tl e d d o w n o n t h e c u lt c h e s w h i c h w e r e p r e v i o u sl y

F C C L O C M F C C

A R

F i g . 2 . S k e t c h s h o w i n g t h e s e a - f a r m i n g s e t - u p (n o t to sc a le ). A b b r e v i a t i o n s : F C C - -F i s h - ca g e c u l tu r e ; L O C - L o n g - l i n e o y s t e r c u lt u re ; M F C C - M o d i f ie d f is h -c a g ec u l t u r e ; R - - A r t i f i c i a l r e e f.


9/18

Systematic approach o f sea-farrning in Penghu. Taiwan, RO C 2 6 1fL, e d o n a w i r e s t ri n g w i t h a d i s t a n c e o f a b o u t 2 0 c m b e t w e e n t h e m .T h e f ir st y e a r ' s w o r k o f t h e p r e s e n t s t u d y b e g a n i n O c t o b e r 1 9 8 2 , b u tc u l t u r e s y s te m s w i th o y s t e r s pa ts w e r e n o t s e t u p t ill F e b r u a ~ 1 9 8 3 ,o w i n g to t h e p r e v a i li n g m o n s o o n . I n 1 9 8 4 t h e sy s te m s w e r e s et u p i nF e b ru a ry . f o r t h e s a m e r e a s o n . T h e o y s t er s w e r e r a n d o m l y c o l l e c te dm o n t h ly . T h e n u m b e r o f cu l tc h e s p e r s t ri ng a n d t he g r o w t h p a r a m -e t e rs o f o y s te r s w e r e r e c o r d e d . R e s u l ts o f th e p r e s e n t s t u d y w e r e c o m -p a r e d w i t h th e e a r l i e r d a t a ( L i n a n d T a n g , 1 9 8 0 ; d a t a c o l l e c t e d inm o n o - c u l t u r e i n t h e s a m e w a t e r s w h e r e t h e p r e s e n t s t u d y w a s m a d e )t o c la r if y t h e e f fe c t o f p o l y - c u l t u r e o n t h e p r e s e n t w o r k .

R e s u l t s s h o w e d t h a t t h e h a r v e s t i n g s e a s o n c o u l d b e s a i d t oc o m m e n c e a t f i v e m o n t h s a f t e r t h e s p a t s w e r e i n t r o d u c e d ( T a b l e s 2a n d 3 ). B e f o r e J u l y , a d is t in c t i n c r e a s e i n s h e ll l e n g t h c h a r a c t e r i z e do y s t e r g r o w t h , w h e r e a s t h e g r o w t h o f v i sc e r al m a s s w a s r e t a r d e d c o m -p a r e d w i t h t h e i n c r e a s e i n s h e l l l e n g t h . I n J u n e , t h e s h e l l r e a c h e d al e n g t h o f 6 c m , a v a l u e g r e a t e r t h a n t h o s e o f th e o y s t e r s h a r v e s t e d i nw e s t e r n T a i w a n ; h o w e v e r , th e s e o y s t e r s w e r e n o t s u i t a b le t o m a r k e td u e t o t h e i r s m a l l si ze . A f t e r J u n e , t h e w e i g h t o f v i s c e ra l m a s si n c r e a s e d a t a g r e a t e r r a te t h a n p r e v io u s l y . T h i s i n c r e a s e i m p r o v e d t h eq u a l i t y o f t h e s e o y s t e r s . T h e a v e r a g e w e i g h t o f v i s c e r a l m a s s o f a n

T A B L E 2S h e ll W i d t h ( c m ) o f O y s t e r s F o u n d o n t h e L o n g -l ine Cul ture at Da gu oye h, Peng hu, Du ring1983-84

M onth 1983 1984F e b r u a r y - - 1 .0M a r c h 0 . 7 i -5A p r i l 1 .2 1 -8M a y 2 . 5 2 .3June 2.8 3.0Ju ly 4 - 1 3 " 4A u g u s t 4 - 0 3 "7S e p t e m b e r 3 .8 - -O c t o b e r 3 '5 - -N o v e m b e r 3-9 - -D e c e m b e r 3 .5 - -


10/18

262 K . - H . C h a n g J . - C L e eT A B L E 3

M e a n W e ig h t ( g ) o f V i s c e r a l M a s s o f Oysters inLong-fine Culture at Daguoyeh. Pe nghu , During1983-84

M on th 1983 1984May -- 0-9June -- 1"8July 3' 1 2.8September 4.3 2-7O ctober 4-0 --November 5-1 --December 4.0 --

o y s t e r w a s 3-5 g i n A u g u s t . I n O c t o b e r , t h e w e i g h t re a c h e d a p e a k ,g e n e r a l l y a r o u n d 5 g .

T o c o p e w i t h t h e s e g r o w t h p a r a m e t e r s , t h e h a r v e s t i n g s e a s o n f o ro y s t e r s s h o u l d c o m m e n c e i n A u g u s t a n d e n d i n O c t o b e r , w h e n t h en o r t h e a s t e r n m o n s o o n t e n d s t o p re v ai l .

T h e l os s o f o y s t e rs o c c u r r e d o n a s m a l l s ca le , w h e n c o m p e t i t i o nf o r s p a c e t o o k p l a c e a m o n g i n d iv i d ua l s . H o w e v e r , p r e d a t i o n f r o ml e e ch e s c o n t r i b u t e d t o m u c h o f t h e d a m a g e t o o y st er s . I n o u r s t u d y t h el e e c h w as s e l d o m f o u n d w i d e l y d i s t r i b u t e d a n d c o n s u m i n g o y s t er s int h e s e a b e f o r e A u g u s t . B u t i n A u g u s t t h e r e w e r e s ix le e c h e s e s t im a t e do n e a c h s t r in g o f o y s te r s. T h e e x p a n s i o n i n th e n u m b e r o f l e e c h esm i g h t b e d u e t o t h e i r h ig h r e p r o d u c t i v e r a te ; in th e l a b o r a t o ~ ' a l e e c ho f 2 0 c m 2 ( s u r fa c e a r e a) w o u l d s p a w n a t o t a l o f 4 5 0 0 0 0 e g gs f r o mA u g u s t to N o v e m b e r .F i s h - c a g e c u l t u r eR e a r i n g f i s he s in a f l o a ti n g c a g e in t h e w a t e r s l e e w a r d o f D a g u o y e hh a s g r e a t p o t e n t i a l . I n c a g e c u l t u r e , f i s h e s a r e r a i s e d i n a n e t c a g ea n c h o r e d t o th e s e a f lo o r. B u o y s f a s t e n e d w i th l u m b e r k e e p t h e c a gef l o a t i n g , t o l e a v e t h e n e t i m m e r s e d i n t h e w a t e r . W a t e r s m o v e i n a n do u t o f t h e c a g e -n e t , e n s u r i n g a n a d e q u a t e o x y g e n c o n t e n t fo r t h e c ap -t iv e s . I n t h e p r e s e n t s t u d y f i v e s q u a r e c a g e s ( 6 m x 6 m x 6 m ) w e r ee m p l o y e d .


11/18

Systematic approach o f sea-farming in P enghu, Taiwan. RO C 263F i s h es c u l t u r e d i n th e c a g e c o m p r i s e d g r o u p e r s , Epinephelus spp . ,

a n d Plectropomus leopardus; s e a - b r e a m , Chr3. soph us m ajo r.Acanthopagrus schlegeli , a n d A. latus; s n a p p e r s , Lut]anus russelli , a n dL. argentimaculatus; e m p e r o r f i s h , Lethrinus choerorhynchus; a n dr u d d e r f i s h , G irella punc tata. A f t e r t h e s e f i s h e s w e r e c u l t i v a t e d f o r ap e r i o d o f 1 0 t o 1 6 m o n t h s , g r o w t h p a r a m e t e r s o f sLx o f t h e m w e r e c a l-c u l a t e d i n t e r m s o f s u r v i v a l r a t e a n d g r o w t h r a t e . T h e h i g h e s t s u r v i v a lr a t e w a s a t t r i b u t e d t o g r o u p e r s ( 8 1 ' 4 % ) , w h e r e a s r u d d e r f i s h h a d t h el o w e s t , th a t i s, o n l y 3 8 " 4 % o f r u d d e r f i s h i n d i v i d u a l s s u r v i v e d ( T a b l e 4) .A r t i f i c i a l r e e f s f o r f i s h e s

E m p l a c e m e n t o f a r t i f i c i a l r e e f s i n t h e s e a i s a n o t h e r w a y t o f a r mb e n e a t h t h e w a v e s . O v e r t h e p a st 1 0 y e a r s w e h a v e g a i n e d e x p e r i e n c ei n t h e c o n s t r u c t i o n o f a r t i f i c i a l r e e f s , a n d c l e a r c u t c r i t e r i a a n d g u i d e -l in e s h a v e b e e n s u g g e s t e d t o e n s u r e a n e f f ic i e n t i n v e s t m e n t .

P r e v i o u s l y t h e a r ti fi ci al r e e fs w e r e m a i n l y e m p l a c e d o n t h e o p e ns a n d y b o t t o m . H o w e v e r , i n a p o l y - c u l t u r e s y s te m , t h e f a c to r s a f f ec ti n gt he b i o lo g ic a l c o m m u n i t y a r o u n d t he r e e f a re a a r e m o r e c o m p l ic a t e d .

I n th e p r e s e n t s t u d y t h e a r ti fi ci a l r e e f s w e r e e m p l a c e d n e a r l o n g - l in eo y s t e r c u l tu r e s y s te m s . D a t a c o l l e c te d w e r e c o m p a r e d w i t h t h o se f r o mt h e re e f s e m p l a c e d i n t h e s a m e b a y b u t 4 k m a w a y . T h e r es u lt s sh e ds o m e l i g h t o n t h e e f f e c t o f t h e l o n g - l i n e o y s t e r c u l t u r e s y s t e m o n t h ea r ti f ic i al r e e f c o m m u n i t y .

C o n c r e t e b l o c k s o f 1 m 3 w e r e e m p l o y e d a s r e e f m a t e r ia l s F i g . 3).W i th a v i ew t o i m p r o v i n g t h e p r o d u c t i o n o f r e e f f is h es s u c h ass n a p p e r s a n d g r o u p e r s , t h e a r ti fi ci al r e e f w a s d e s i g n e d w i t h an i n n e rs p a c e a s s h o w n i n F i g . 3. T h e s p a c e s e r v e d a s a s h e l t e r f o r th e s e t a r g e tf is h es . B e c a u s e o f t h e h i g h t u r b i d i t y o f l o c a l w a t e r s a n d t h e r a r i ty o fpe l a g i c f is he s he r e , t he a r t if i c ia l r e e f w a s no t e m p l a c e d t o a c t a s a la ndm a r k f o r p e l a g ic fi sh e s . T h e r e e fs w e r e i n s t e a d c a r e f u l ly e m p l a c e d o nt h e s e a b o t t o m , w i t h l it tl e o v e r l a p p i n g . A t o ta l o f 2 3 4 r e e f b l o c k s w a sus e d i n t h i s s tudy .

T h e s e a rt if ic ia l re e fs w e r e e m p l a c e d in w a t e rs 1 2 - 1 5 m i n d e p t h .B u o y s w e r e a n c h o r e d t o i n d i c a t e th e e x a c t s it e fo r l a te r in v e s t ig a t io n .A f t e r r e e f e m p l a c e m e n t t h e b io t a a r o u n d r ee fs w e r e m o n i t o r e d , a sw e l l a s fi sh s p e c i e s c o m p o s i t i o n a n d t h e i r s t a n d i n g c r o p s . I n th e i n-v e r t e b r a t e c o m m u n i t y , b r y o z o a n s w e r e t h e f i r s t t o s e t t l e o n t h e s u b -


12/18

I..}

TABLE4

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(2V.*;Op]3'S111l1"

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850

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620

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13/18

System atic appro ach o f sea-farming in P enghtt, ~li~{ltz, 1~0C 2 6 5

o '\ I0 . 3M

1 M ~

_ '3

lF i g . 3 . S c a l e o f a r t i f i c i a l r e e f .

m e r g e d a r ti fi ci al re e fs . T h e s e b r y o z o a n s w e r e a ls o c o m m o n o n o y s t e rs h e l ls h a n g i n g o n t h e l o n g - l i n e .A l a ye r o f th e i m m i g r a t in g b r y o z o a n s w a s f o u n d f o r m i n g o n t h ec o v e r o f r e e f s 2 0 d a y s l a t e r . A f t e r t w o m o n t h s t h e s e b r y o z o a n s t e m -p o r a r i l y d o m i n a t e d t h e i n v e r t e b r a t e c o m m u n i t y . H o w e v e r . f o u l i n go r g a n i s m s s u c h a s s p o n g e s , o c t o c o r a l l i a , a n d s e a s q u i r t s g r a d u a l l yi n v a d e d t h e b io t a . T h e y c o m p e t e d f o r s u b s tr a t e s, d i v e r s i f y in g t h e lo c a li n v e r te b r a te c o m m u n i t y .

A r i c h v a r i e t y o f f is h e s o c c u r r e d i n t h e r e e f ar e a . S n a p p e r Lz~ t jan ,srz~sselli c a m e f ir st a n d r e m a i n e d t h e r e a s b y fa r th e m o s t a b u n d a n t int h e f o l l o w i n g d a y s .O t h e r s o f h ig h e c o n o m i c v a lu e w e r e g r o u p e r s, f o r e x a m p l e E p i n e -p h e h t s d i a c a n t h u s , a n d E. lat i faciatus, w h i c h a p p e a r e d s p o r a d i c a l l y

a r o u n d t h e r e e f s . B a r r a c u d a S p h r a e n a s p p . s c h o o l e d i n t h e w a t e rc o l u m n a b o v e t h e r e e f s ; l i o n f i s h Pterosis radiata , f i lef ish SteJzphano-lepis cirrhifer, a n d h a w k f i s h Cirrhi t ichthys serratus w e r e als o c o m m o nin t h e f is h c o m m u n i t y a r o u n d t h e r e e f a re a d u r i n g t h e f ir st y e a r o f c o n -s t r uc t i on .T o f i gu r e ou t t he r o l e o f a r t i f i c i a l r ee f s i n f i s h s u r v i va l i n t he en -v i r o n m e n t , s n a p p e r Lztt janlts rztssel l i w e r e s p e a r e d d u r i n g th e d a y a n d


14/18

66 K.-H. Chang, J.-C. Leetheir stomach contents were analyzed. Surprisingly, among fivespeared individuals, two with empty stomach and gut were found. Theother three had crabs (decapods) detritus remaining in their stomachs.The result suggested that Lrctjanrcs russelli were nocturnal fish. Arti-ficial reefs acted as shelters for this fish during the day. The fish wouldspread out to hunt for food at night. Therefore it was the space factorin the artificial reefs that contributed to the survival of the main fish inthis reef area.

HARVEST FROM THE SEA-FARMING SYSTEMLong-line oyster cultureIn the present study the oysters put into cultivation in January 1983were harvested in August of the same year. The damage caused byoyster leeches advanced the date for harvesting. Catch statisticsshowed that in 1983 6000 kg of oysters were harvested in each set oflong-line systems. Therefore a total of 60 000 kg of oysters was esti-mated over the 10 sets of culture systems. Unfortunately leeches con-sumed 40% of the edible part to leave only 0.7 kg collected out of astring of oysters. The total weight of the edible part taken from all theoysters was therefore estimated as 3500 kg in the experimentalculture systems. The value of the harvested oysters was economicallybalanced to the cost of building up the long-line culture systems whichwere durable enough to use for the subsequent culture.

Artificial reefsFish standing crops monitored by divers clearly demonstrated that thebiomass increased significantly, in comparison with that occurring inthe barren sea before reef emplacement. The biomass of fishesattracted to each block of artificial reef was estimated to be in a rangebetween 4 kg block- * and 13 kg block- in the fourteenth month aftercast. The average biomass of fishes for each block was 6.3 kg block-.This was also the value applying per cubic meter, the unit on whicheach reef was made. The biomass around the reef area was thereforetotaled at 1474 kg as calculated by the quantity of the reefs emplaced.Catches by local fishermen were not a problem because the site where


15/18

Systematic approach o f sea-farming in Penghu, Taiwan, RO C 267the reefs were emplaced was not open to them till the experiment wascompleted.

DISCUSSIONThis study tries to elucidate the functional connections between typesof mariculture and their environment. However, information collectedduring the first two years is still not enough to shed full light on this.

A remarkable feature of the water in this area was its notable tur-bidity. The water bathing the oysters had a dark-grey colour so that asubmerged Secchi disc soon disappeared from sight, and the turbidityincreased near the sea bottom. This turbidity was caused by finely-dispersed silt and particulate matter which were kept perpetually inmotion by the currents. Though no exact data on the quantities ofsediment per volume of water were available, it was quite sure that thefigures in Datsang Bay were considerably higher than other areas. Thepoor turn-over rate of the waters, due to the semi-closed topographyof the bay, was thought to be connected with the accumulation of thesuspensions. Without any doubt the filtering activity of oysters andother kinds of molluscan shellfish which abound there greatlypromoted sedimentation.In the present study culture of oysters depended mainly upon theoccurrence of plankton, an organism derived from natural prolificacy.It is generally postulated that the phytoplankton have to find a sourceof nutrients such as nitrogen, phosphorus, silicon, and other oligo-elements in the marine environment. A lack of some of these elementswill retard their growth rate (Bougis, 1976). In the present studynitrogen existed in different formations, but with a total concentrationwithout apparent seasonal variation. The low concentrations of P Q - Pin January 1984, and SiO 2 in April, May, and June 1984, might pre-sumably limit the succession of phytoplankton. The abundance ofphytoplankton observed in the local waters was, however, by nomeans in agreement with this assumption. The linkages betweennutrients and phytoplankton growth were still too ambiguous to beexplicable according to the present results. Further analysis requiresthe addition of data collected in the third consecutive year. No figureshave been obtained on the amount of plankton consumed by the localoysters. But the excellent growth rate of the bivalve farmed in this area


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268 K.-H. Chang, J.-C Lee(cf. Lin and Liang, 1982) suggests that sufficient quantities of phyto-plankton must have been available for months in succession. In fact,the abundance ofphytoplankton in the area where the long-line oysterculture was located was less than those investigated elsewhere. Thisimplies that a conspicuous amount of phytoplankton has been con-sumed by the oysters.Though the abundance of phytoplankton in 1983 was much lowerin comparison with that of the following year, there was no evidence ofretardation of growth of the oysters farmed in 1983. It implies that thislow abundance of phytoplankton in 1983 did not act as a limitingfactor pertaining to this plankton-filter. However, mortality wasdetectable in the cultured oysters. Mortality might be due to thecompetition for space between con-specifics or hetero-specificsduring the growing period, or to predation from leeches in August.The property of filtering phytoplankton leaves oysters to serve asan "energy accumulator ' as some mussels do, since phytoplankton actsas the leading role in primary production in the ocean. At present, tocultivate oysters seems to be very promising, because investment isseldom required for directly enhancing the food supply for oysters,but mainly for spat collection and the culture systems. Natural proli-ficacy would reinforce food for routine consumption, demandingfewer subsidies to cultivate oysters. The heavy excretion of oystersmight be troublesome in an environment with a low function rate ofself-clean activity. In the present study the comparatively high CODvalues in the sediments accompanied with low nutrient concentrationsin the water suggested that the degradation of the excreted materialwas under way, but at a slow rate. However, the dissolved oxygen inthe water maintained at a level of 80% saturation would benefit oysterculture in the local waters.Establishing man-made habitats for fishes has been proved to be anefficient way to increase fisheries production around Taiwan (Chang,1976, 1977, 1979, 1980). The succession of organisms around artifi-cial reefs in the present study was similar to that found around reefsemplaced at Soukang and Datsang Bay in 1977. Comparing theresults from Daguoyeh and Soukang, a general conclusion wasreached that the success of the biotic community around artificialreefs was mainly condi tioned by its environment. Thus artificial reefsemplaced in a similar environment would result in a similar success for


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Systematic approach o f sea-farming in Penghu, Taiwan, RO C 269the fish community, and the same would apply to the invertebratecommunity.In the present study, long-lines of oyster culture systems seemed notto affect the effectiveness of artificial reefs profoundly. This might bedue to the following two reasons. One is that high turbidity of the localwaters meant the waving and the shadow were i~ored. Otherwise, ifthe water was clear enough, or long-lines were close enough, the long-lines in the water colunm would wave like a net to induce escapingbehavior of pelagic fishes. The other possible reason is that the resi-dents had become familiar with the waving and shadow effects. Basedon the second explanation, it would take time for fishes to adjust. Butthe mass appearance of Lutjanus msselli around the newly emplacedreefs in the present study seemed to contradict this hypothesis. Afurther discussion relies on collecting further information. An experi-ment aiming at a solution of this problem will be initiated as soon aspossible in the future.

CONCLUSIONSAs tropical warm water surrounds the whole of Taiwan, the marinefauna and flora in this area has its distinctive characteristics. Underthe corporate efforts of the scientists of research institutions andadministrators of concerned authorities, the development of sea-farming in the Taiwan area has progressed rapidly.To ensure an adequate sea-farming procedure and to prevent theenvironment from deterioration, efforts to study the interactionbetween culture applications and the environment is underway. Thisfundamental work will provide mean in~ul data for sea-farming in thefuture and will be worthwhile for creating a commercially viableoperation.

ACKNOWLEDGEMENTSThis work has been sponsored by the Committee of Agriculture(formerly the Council for Agricultural Planning and Development),Executive Yuan, since September 1982. Our thanks are due to the fol-


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270 K.-H. Cha ng, J . -C. Leel o w i n g p e o p l e , w h o h a v e k i n d l y p e r m i t t e d t h e c i t a t io n o f t h e i r u n-p u b l i s h e d d a ta : D r s I - M i n g C h e n a n d L e e - S h i n g F o n g , N a t i o n a l S u nY a t - s e n U n i v e r s i t y , o n w a t e r q u a l i t y ; D r R a n g H u a n g , a n d P r o f e s s o rY a o - S u n g L i n , N a t i o n a l T a i w a n U n i v e r s i t y , o n p h y t o p l a n k t o n a n dl o n g - l i n e o y s t e r c u l t u r e , r e s p e c t i v e l y ; a n d S i n g - H a w H u , d i r e c t o r ,D i v i s i o n o f P e n g h u , T a i w a n F i s h e r i e s R e s e a r c h I n st it u te , o n c a g ec u l t u r e . H e l p f r o m t h e d i v e r t e a m o f t h e I n s t i t u t e o f Z o o l o g y ,A c a d e m i a S i n ic a , o n f i el d w o r k is a ls o d e e p l y a p p r e c i a t e d .

R E F E R E N C E SBougis. R (1976). M a r i n e P l a n k t o n E c o l o g y , Elsevier Science Publ ishingCom pany, New York , 355 pp .Chang, K. H. (1976). Artificial reefs in Taiwan (I). M o n o g r a p h S e r i es N o . 1 ,Institute of Zoolog y, A ca de m ia Sinica, 80 pp.Chang, K. H. (1977). Artificial reefs in Taiwan (II). M o n o g r a p h S e r i e s N o . 2 ,Ins ti tute of Zoology, Aca dem ia Sinica, 49 pp.Chang, K. H. (19 79). A rtificial reefs in Taiwan (III). M o n o g r a p h S e ri es - N o . 7 ,Ins t itute of Zoolog y, Ac ad em ia Sinica, 150 pp.Chang, K. H. (1980). Tow ard th e sea farm ing-art if icial reefs in Taiwan. S y m -p o s i u m o n a q u a c u l t u r e i n w a s te w a te r , N a t i o n a l In s t it u t e f o r W a te r R e s e a r cho f th e C S I R , 24 -26 No vem ber 1980 , Pre toria , 23pp .Chang, K. H., Chen, C. P., Hsieh, H. L., Su, W. C., Hu, S. H. & Lee, S. C.(1981). O ccu rrenc e of juven i le pen aeid shr imps in the inter tidal area ofChi to B ay , Penghu, Taiwan. B u l l . I n s t . Z o o l . , A c a d e m i a S i n i c a , 20 (2) ,1 -10 .Chang, K. H., Chen, C. R, Hsieh, H. L., Su, W. C., Hu, S. H. & Lee, S. C.(1982). Spec ies com po sit io n and spatial d is tr ibution of infaunal bivalves inthe intert idal f lats of Penghu. B u l l . I n s t . Z o o l . , A c a d e m i a S i n i c a , 21 (1),

1-8.Hsieh, H. L., Che n, C. P. & C hang , K. H. (1981 ). T h e gro wth an d p rod uc tiono f G a f r a r i u m t u m i d u m (Ro ding) (Bivalve) in the l i ttoral zo ne of Ch iang-Mei, Penghu. B u l l . I n st . Z o o l . , A c a d e m i a S i n ic a , 20 (2), 11-20 .Lin, Y. S. & Liang, M. H. (1982). Growth and sett ing of cultured oysterC r a s s o st re a g ig a s T h u n b e r g in Putai Ba y. B u l l . I n st . Z o o l . , A c a d e m i a S i n ic a ,21 (2) , 129 -43 .Lin, Y. S. & Tang, H. C. (1980). Biological studies on cultured oysters in1~ - __ .enghu. B u l l. I n st . Z o o l . , A c a d e m i a S i n i ca , 19 (2), - 99

Chang 1986 Aquacultural-Engineering

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